Unfortunately, we do not provide data prior to 1980 due to difficulty in verifying their accuracy. We do provide real GDP growth rates in the WEO publication, figure 1.1. You may download the data from here. But we do not have data for World nominal/current GDP in USD.

The United Nations Common database is free to access and provides nominal USD GDP data for most of the countries in the world from 1970. You should be able to use their country-level data and aggregate/sum across countries to create your own estimate of World GDP, given sample-consistency issues from year-to-year.

Hope this helps somewhat. Let us know if you have any other questions.